Brake control apparatus for railway cars

ABSTRACT

A brake control apparatus for railway cars having sprung and unsprung portions is interposed between a brake pressure supply line and a brake cylinder line. A first chamber is connected to the brake pressure supply line and a second chamber is connected to the brake cylinder line. The chambers are abutted by surfaces having different cross-sectional areas of a diaphragm which is biased. A first valve responsive to positioning of the diaphragm, and a second valve responsive to positioning of a strut in a strut cylinder, effect first and second predetermined relationships between pressure drop in the brake pressure supply line and pressure drop in the brake cylinder line. The strut cylinder, mounted between the sprung and unsprung portions of the railway car, may be adapted to sense partially loaded as well as fully loaded or unloaded conditions.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending application Ser. No.775,379, filed Mar. 7, 1977, now U.S. Pat. No. 4,143,923.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates generally to brake control devices, and moreparticularly to a brake control apparatus responsive to loadingconditions of railway cars.

One of the successful brake control devices for railway cars has beenthe well-known AB freight brake control device. However, the AB brakecontrol is a single capacity device which applies a given brake signalto each car of a train without regard to the loading of the car. Theundesirable result in a train comprised of loaded and unloaded cars is ashock or buffer effect which occurs because of inadequate braking on theloaded cars and excessive braking on the unloaded cars. Thus, a needexists for a brake control device for railway cars which applies thebrakes of each individual car in accordance with the loading conditionsthereof.

Many types of brake control apparatus have been heretofore known andused for automatically reducing the degree of braking on railway carscarrying a light load and thereby avoiding excessive braking on thewheels of relatively lightly loaded cars. Previous types of doublecapacity brake control apparatus usually comprise a so-calledchange-over valve device and strut cylinder for measuring the degree ofload carried by a railway car according to the relative positioning ofsprung and unsprung portions of the railway car undercarriage. Theseprior devices, sometimes referred to as empty and load brake controlapparatus, have generally been relatively complicated in nature and highin cost.

Furthermore, most of the heretofore known empty and load brake controlapparatus for railway cars are changed over to provide either empty orload braking, accordingly as the vehicle is empty or loaded, only whilethe train brake pipe pressure is increasing subsequent to a brake pipepressure reduction to substantially zero, a condition obtained underemergency brake application and not during a full or partial servicebrake application.

Recognizing that railway cars are often operated partially loaded, aswell as fully loaded or fully unloaded, it is the general purpose ofthis invention to provide brake control apparatus for railway cars whichis responsive to the degree of loading in each individual car to effectproficient brake application in loaded, unloaded and partially loadedrailway cars, thereby preventing the undesirable buffer effect along thetrain caused by uneven brake application, and which continuously sensesthe condition of loading during emergency and service brake application.

Another purpose of the invention is to provide brake control apparatuswhich may readily and economically be combined with existing railwaybrake valve devices, such as for instance the widely used AB brakevalve, without requiring changes in train operating procedure. Theinvention functions equally well whether the train brakes are applied bya single pressure reduction, or more typically, by staged pressurereductions.

More specifically, the present invention comprises a brake control valveinterposed between a brake pipe and a brake cylinder line. The controlvalve includes a moveable diaphragm assembly suspended therein whichseparates two chambers connected to the brake pressure pipe and thebrake cylinder line, respectively. The diaphragm is responsive to loadsensing strut cylinder mounted between the sprung and unsprung portionsof the railway car undercarriage to actuate other valves within thecontrol valve in order to effect a relatively reduced braking signal foran unloaded railway car with respect to the braking signal for a loadedrailway car.

A given brake pipe signal may be either reduced to effect brakeactuation on an unloaded railway car, or increased to effect brakeactuation on a loaded railway car. In the former case, a limiting valvemay be provided between the control valve and the strut cylinder of theapparatus to prevent pressure reduction below a predetermined safetylevel. In the latter case, a limiting valve may be provided across thestrut cylinder and the control valve of the invention to allow, underemergency conditions, the brakes of unloaded railway cars to be actuatedto be the same degree as the brakes of loaded railway cars. In bothcases, the strut cylinder may be adapted to sense the degree of railwaycar loading, thereby enabling the apparatus to initially effect brakeactuation on a partially loaded railway car as though the car were fullyloaded, with final actuation effected at a lower value as though the carwere unloaded. Also in the latter case, there may be provided anemergency pressure source, if desired.

DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be had by referenceto the following Detailed Description when taken in conjunction with theaccompanying Drawings, wherein:

FIG. 1 is a vertical cross-sectional view of a brake control apparatusfor railway cars incorporating a first embodiment of the invention;

FIG. 2 is an enlarged vertical cross-sectional view of a firstmodification of the brake control apparatus of FIG. 1;

FIG. 3 is a side view of a railway car undercarriage in which certainparts have been broken away more clearly to illustrate the placement ofa load sensing strut cylinder on the bolster;

FIG. 4 is a portion of an end view of a railway car undercarriage takenalong the line 4--4 of FIG. 3 and showing a load sensing strut cylindermounted on a bolster;

FIG. 5 is a vertical cross-sectional view of a brake control apparatusfor railway cars incorporating a second embodiment of the invention; and

FIG. 6 is an enlarged vertical cross-sectional view of a firstmodification of the brake control apparatus of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the Drawings, and particularly to FIG. 1 thereof, thereis shown a brake control apparatus for railway cars 10 incorporating theinvention. The brake control apparatus 10 comprises a control valve 12,a pressure limiting valve 14 and a strut cylinder 16. Brake controlapparatus 10 is interposed between a brake pipe 18 and a brake cylinderline 20. Brake pipe 18 runs along the entire length of the train ofrailway cars and is connected to a remote source of fluid under pressure(not shown) by means of a brake application valve (not shown). The brakecylinder line 20 serves to connect the brake control apparatus 10 with aconventional brake cylinder (not shown).

Control valve 12 is of sectionalized casting construction, consisting ofan upper casing section 22, intermediate casing section 24 and lowercasing section 26. Casing sections 22, 24 and 26 are attached one toanother. Plug member 28 is threadedly engaged through the bottom end oflower casing section 26.

Disposed within the control valve 12 is diaphragm assembly 30. Diaphragmassembly 30 includes a pair of spaced diaphragms, 32 and 34. The outerperiphery of the first diaphragm 32 is clamped between the lower face ofintermediate casing section 24 and the upper face of lower casingsection 26. Similarly, the outer periphery of second diaphragm 34 isclamped between the lower face of upper casing section 22 and the upperface of intermediate casing section 24.

The inner peripheries of diaphragms 32 and 34 are secured withindiaphragm assembly 30. The inner periphery of first diaphragm 32 isclamped between the lower face of diaphragm follower 36 and the upperface of lower diaphragm nut 38 which threadedly engages a downwardlyprotruding threaded portion of diaphragm follower 36. In a similarmanner, the upper face of diaphragm follower 36 includes an upwardlyprotruding threaded portion on which is threadedly engaged upperdiaphragm nut 40. Hence, the inner periphery of second diaphragm 34 issecurely clamped between the lower face of upper diaphragm nut 40 andthe upper face of diaphragm follower 36. Thus it is seen that diaphragms32 and 34 flexibly suspend diaphragm assembly 30 for limited axialtranslation within the sloped annular space 41 between diaphragmassembly 30 and intermediate casing section 24.

Diaphragm follower 36 includes a bore 42 positioned coaxiallyintermediate upper counterbore 44 and lower counterbore 46. Slidablydisposed within bore 42, and extending through counterbores 44 and 46,is valve stem 48. Upper counterbore 44 extends upwardly from bore 42 andterminates in a valve seat 50 located in the end surface of the upperthreaded protrusion of diaphragm follower 30. Valve seat 50 serves toreceive valve member 52, which is rigidly secured to valve stem 48 at apoint below the upper end thereof. Lower counterbore 46 extendsdownwardly from bore 42, terminating at the end of the lower threadedprotrusion of diaphragm follower 36. A packing nut 54, through whichvalve stem 48 is slidably received, threadedly engages the outer portionof lower counterbore 46 to compress and retain packing material 56therein. As a means of preventing undesirable pressure losses due toaccidential displacement of packing material 56 caused by thedisengagement of packing nut 54 during service, lower diaphragm nut 38includes a coaxial bore 58 having an inside diameter less than theoutside diameter of the collar of packing nut 54. As a result, lowerdiaphragm nut 38 serves both to retain packing nut 54 and to prevent itscomplete disengagement from counterbore 46. Therefore, it will be seenthat valve stem 48, which is slidably disposed in bore 42 as well aspacking nut 54, extends completely through diaphragm assembly 30.

Also included in diaphragm follower 36 of diaphragm assembly 30 are leftand right cross bores, 60 and 62, respectively, both of which open intocounterbore 44 at their interior ends. Right cross bore 62 serves tocommunicate upper counterbore 44 with a cavity 64 formed betweendiaphragm follower36, first diaphragm 32 and lower diaphragm nut 38.Port 66 connects cavity 64 in turn through the outer surface of lowerdiaphragm nut 38. A check valve 68 comprising a spherical member 70biased against the entrance of right cross bore 62 onto cavity 64 byspring 72 functions to close off cavity 64 from upper counterbore 44under certain conditions. Left cross bore 60, on the other hand, unitesupper counterbore 44 with conduit 74, one end of which is secured todiaphragm follower 36. The other end of conduit 74 leads to limitingvalve 14 through an opening 76 in intermediate casing section 24 ofcontrol valve 12. Opening 76 is sufficiently large to permit translativemovement of conduit 74 simultaneously with movable diaphragm assembly30, to which it is attached.

Still having reference to FIG. 1, diaphragm assembly 30, by virtue ofits position within control valve 12 separates the interior volumethereof into two chambers, 78 and 80. Pressure supply chamber 78 isdefined by the lower surface of diaphragm assembly 30, in conjunctionwith lower casing section 26 and plug member 28. The effective area ofdiaphragm assembly 30 abutting pressure supply chamber 78 is thus thearea across the enlarged mouth of lower casing section 26. Stops 82 areprovided around the horizontal rim of lower casing section 26 to limitdownward displacement of diaphragm assembly 30, as well as to preventpressure tight engagement between lower diaphragm nut 38 and the innerrim of lower casing section 26. A port 84 within the wall of lowercasing section 26 opens into a conduit 86 which connects with brake pipe18. Consequently, fluid communication is directly established betweenpressure supply chamber 78 and brake pipe 18.

Located at the bottom end of pressure supply chamber 78, plug member 28is threadedly engaged through the end of lower casing section 26. Anannular gasket 88 is provided for clamping, sealing engagement betweenthe exterior end of lower casing section 26 and the collar of plugmember 28 to preclude leakage of fluid under pressure from chamber 78 toatmosphere.

Plug member 28 includes substantially centrally located bore 90 andcoaxial counterbore 92, whose intersection forms a valve seat to receivevalve member 94. Extending downward from its slidable connection indiaphragm assembly 30 is valve stem 48, the end of which is attached tothe valve member 94 that seats in plug member 28. Bore 90 connectscounterbore 92 opening onto pressure supply chamber 78 with one end ofcross bore 96. The other end of cross bore 96 leads to conduit 98 whichis attached to a bore 100 positioned in upper casing section 22.Accordingly, it will be appreciated that fluid communication may beestablished via conduit 98 between pressure supply chamber 78 andcontrol chamber 80 subject to the action of valve 94.

Control chamber 80 is defined as that volume existing between the end ofupper casing section 22 and the movable abutment formed by the top endof diaphragm assembly 30. It will be noted that the effective area ofthe upper end of diaphragm assembly 30 abutting control chamber 80 isless than the effective area of the lower end of diaphragm assembly 30abutting pressure supply chamber 78. Port 102 located in the wall ofupper casing section 22 allows for direct fluid communication betweencontrol chamber 80 and a brake cylinder (not shown) via brake line 20.Coil spring 104 is disposed within control chamber 80 intermediate upperdiaphragm nut 40 and spring follower 106. The spring follower 106 has adepression in its upper surface for receiving and centering springadjusting screw 108, which is threadedly mounted substantially centrallythrough the upper casing section 22. Thus, by means of spring adjustingscrew 108, the downward biasing force of spring 104 against diaphragmassembly 30 may be set to a predetermined value and/or adjusted form theoutside of control valve 12 without disassembly thereof. A protectivejam nut 110 threadedly engages the exterior protruding end of springadjusting screw 108 to lock it in any desired position. Gasket 112,placed between jam nut 110 and the exterior of upper casing section 22,forms a seal to prevent leakage of fluid pressure from control chamber80 to atmosphere.

Disposed within coil spring 104 and attached to the top surface of upperdiaphragm nut 40 is guide 114. Aperture 116 in the top end of guide 114serves to receive and guide the uppermost portion of valve stem 48.Control chamber 80 fluidly communicates with the interior of guide 114through port 118. A spring 120, disposed in surrounding relationship tovalve stem 48 between valve member 52 and the inside end of guide 114,biases valve stem 48 downward relative to diaphragm assembly 30. As aconsequence, fluid communication may be established between controlchamber 80 and upper counter bore 44 in diaphragm assembly 30 subject tothe action of valve 52.

Pressure limiting valve 14 includes a body 122 having a first chamber124 and a second chamber 126. Slidably disposed within first chamber 124is a piston 128, from the bottom face of which extends a valve member130. Valve 130 serves to open or close passage 131 joining chambers 124and 126. First chamber 124 connects to a passageway defined by conduit74, which leads to cross bore 60 in diaphragm assembly 30.

Piston 128, slidably positioned within first chamber 124, has aperipheral annular groove in which is disposed an O-ring 132. O-ring 132forms a sliding seal between piston 128 and the interior surface of body122 so as to prevent leakage or fluid pressure from the lower portion offirst chamber 124 to the upper portion thereof. Positioned in the upperportion of first chamber 124, intermediate the top of piston 128 andspring follower 134, is spring 136. Spring 136 is biased to counteractthe force generated by the pressure in the lower portion of firstchamber 124 acting against the bottom face of piston 128. The forceexerted by spring 136 may be preset or adjusted by means of springadjusting screw 138. Spring adjusting screw 138 is threadedly mountedthrough the top end of body 122 and contacts spring follower 134.Consequently, it will be understood that conduit 74 may fluidlycommunicate through first chamber 124 and passage 131 with secondchamber 126 subject to the action of valve 130.

Second chamber 126 opens to a passage way 140 via choke 142, whichfunctions to restrict the rate of fluid flow between passageway 140 andsecond chamber 126. The other end of passageway 140 leads to strutcylinder 16.

Strut cylinder 16 includes a body 144 in which is diposed an extendingstrut 146. Body 144 includes a top chamber 148. A port 150 in the wallof body 144 connects top chamber 148 with passageway 140. Therefore, topchamber 148 of strut cylinder 16 is in fluid communication with secondchamber 126 of pressure limiting valve 14. Bore 152 joins top chamber148 with bottom chamber 154, which opens to atmosphere via port 156.Lower bore 158, which is coaxial with bore 152, slidably engages andguides strut 146 for translation within body 144. The bottom end ofstrut 146 is reduced and threaded to receive a contact nut 160. A valvebody 162 is located in top chamber 148 and is attached near the reducedtop end of strut 146. A spring 164 interposed between the end of topchamber 148 and valve body 162 urges strut 146 downwardly, which movesvalve 162 to a closed position. Preferably, contact nut 160 should beadjusted so that valve 162 is open when the car is loaded at between 40%and 60% capacity. Accordingly, subject to the position of valve 162,passageway 140 may be either closed or open to chamber 148 and 154, andthus to atmosphere.

Turning momentarily to FIGS. 3 and 4 in conjunction with FIG. 1, thereis shown a typical location for a strut cylinder 181 which may besimilar to strut cylinder 16. Railway car 166 is supported atop anundercarriage 168. Undercarriage 168 comprises a transverse truckbolster 170 which supports side truck frames 172. Side truck frames 172are resiliently attached to truck bolster 170 by means of springs 174.Rotatably supported on side truck frames 172 are wheels 176, whichrollingly contact underlying railroad track 178. Strut cylinder 181 ismounted substantially vertically on truck bolster 170, as for instancewith bracket 180. Projecting stop 182 secured to truck side frame 172extends substantially horizontally beneath the strut cylinder 181. Thestrut cylinder 181 is thus mounted on a sprung portion of theundercarriage while its stop 182 is mounted on an unsprung portion ofthe undercarriage 168. Since various loadings in railway car 166 causecorresponding deflections in spring 174 and hence relative displacementbetween sprung and unsprung portions of undercarriage 168, the conditionof loading is sensed by strut cylinder 181.

The parts of the brake control apparatus 10 illustrated in FIG. 1 and sofar described function as follows. Prior to charging the train brakesystem for operation, it will be understood that all cavities andconduits within brake control apparatus 10 are at or near zero gaugepressure. With no pressure in pressure supply chamber 78 to counteractthe downward force of spring 104, diaphragm assembly 30 rests in a downposition against stops 82. Diaphragm assembly 30 thus displaceddownward, valve 94 is closed while valve 52 is open to permit fluidcommunication from upper counterbore 44 through guide 114 and port 118to control chamber 80.

In initially charging the automatic brake control apparatus 10, a remotesource of fluid under pressure (not shown) supplies pressurized fluid tobrake pipe 18. Pressurized fluid flows from brake pipe 18 throughconduit 86 to supply chamber 78 of control valve 12. As the pressurebuilds within supply chamber 78, the resultant upward force on diaphragmassembly 30 overcomes the opposing force of spring 104, moving diaphragmassembly 30 upward. The upward shift of diaphragm assembly 30 causesvalve seat 50 to engage valve 52, thereby closing communication betweenupper counterbore 44 and brake control chamber 80. Further pressure risein supply chamber 78 pushes diaphragm assembly 30 and thus valve stem 48upward beyond the generally central position where valve 52 was closed.Since valves 94 and 52 are both rigidly fixed to valve stem 48, valve 94is therefore pulled open allowing pressurized fluid to enter controlchamber 80 from supply chamber 78 via conduit 98. As this pressurizedfluid fills control chamber 80, a downward force is generated to augmentthe biasing of spring 104. Diaphragm 30 will thus shift to a generallycentral position where the sum of the forces acting downwardly ondiaphragm assembly 30 are precisely balanced by the forces actingupwardly on diaphragm assembly 30. That is, in the balanced positiondepicted in FIG. 1, the upward force generated by the pressure in supplychamber 78 against the lower face of diaphragm assembly 30 cancels thesum of the force of spring 104 and the force generated by the pressurein control chamber 80 against the upper face of diaphragm assembly 30.Therefore, only brake line 20, conduits 86 and 98, and chambers 78 and80 are initially charged to the pressure level of brake pipe 18. FIG. 1depicts brake control apparatus 10 in a charged and ready condition.

When it is desired to set the brakes on an unloaded railway car, fluidpressure in brake pipe 18 is reduced in the usual manner (typically astaged reduction) by operation of a remote brake valve. The same givenpressure drop signal in brake pipe 18 occurs in pressure supply chamber78 which is joined thereto by conduit 86. This drop in pressure inchamber 78 of control valve 12 upsets the force balance on diaphragmassembly 30, which consequently shifts downward from its generallycentral position as it seeks to regain a position of equilibrium. Asdiaphragm assembly 30 shifts downward, it simultaneously translatesalong the axis of valve stem 48. Valve stem 48 remains stationary asdiaphragm assembly 30 slides downwardly therealong because valve 94,which is rigidly attached to valve stem 48, remains firmly seated inplug member 28. However, the downward shift of diaphragm assembly 30disengagement of valve seat 50 from valve 52. Thus, valve 52 opens inopposition to the biasing force of spring 120 which normally urges valve52 into seating engagement within diaphragm assembly 30.

Since valve 52 is now open, fluid communication exists betweencounterbore 44 and control chamber 80 through port 118 of guide 114.Hence the pressure of control chamber 80, which at this time is higherthan the pressure in supply chamber 78 after a given pressure dropsignal, is present in counterbore 44 as well as cross bores 60 and 62,and conduit 74. Fluid at the pressure of control chamber 80 thus enterschamber 124 of limiting valve 14. Valve 130 is normally held open by thepressure of control chamber 80 acting on the bottom face of piston 128against the yielding resistance of spring 136.

It is pointed out that valve 130 closes passage 131 only when thepressure in chamber 124 of limiting valve 14 drops to a level which isinsufficient to resist the downward force of spring 136. In view of thefact that spring 136 may be preset to a desired compression force bymeans of adjusting screw 138, it will be understood that valve 14functions as a safety valve by closing passage 131 when the pressure incontrol chamber 80 drops below a predetermined level. In other words,limiting valve 14 serves as a safety valve for pressure coming down asopposed to pressure going up. It will also be understood that limitingvalve 14 is not essential to the basic operation of brake controlapparatus 10. The presence of limiting valve 14 merely adds a desirablesafety feature.

Assuming, however, that valve 130 and passageway 131 are open,pressurized fluid flows from chamber 124 into chamber 126 and throughpassageway 140 to chamber 148 to strut cylinder 16. Since the railwaycar is unloaded, there is no contact between the end of strut 146 andprojecting stop 182 which would unseat valve 162. Other than beingpressurized to a level corresponding with the pressure in controlchamber 80, and given the fact that chamber 148 is closed at the end ofpassageway 140, no fluid flows through limiting valve 14 to or throughstrut cylinder 16. It will be noted that pressure loss due to excessivevolume of conduits and chambers are negligible in brake controlapparatus 10 when limiting valve 14 and strut cylinder 16 are mounted inclose proximity to control valve 12 in accordance with the preferredembodiment of the invention.

Also opening into counterbore 44 of control valve 12 is right cross bore62, which also senses the pressure of control chamber 80. Check valve 68separates the other end of cross bore 62 from bore 66 opening ontosupply chamber 78. With two unequal pressures acting upon sphericalmember 70 of check valve 68, the greater pressure of control chamber 80prevails to unseat spherical member 70 against the yielding resistanceof retaining spring 72. As a result, fluid passes from control chamber80 through port 118, past open valve 52, through bores 44 and 62, aroundopen valve 68 and into supply chamber 78. In this manner, the pressuredrops and the pressures in chambers 78 and 80 are equalized. Without apressure differential to hold valve 68 open, spring 72 closes valve 68to cut off communication between chambers 78 and 80. Therefore, thebrakes on an unloaded railway car are actuated by the identical pressuredrop signal through brake line 20 as occurred in brake pipe 18.

When it is desired to release the brakes of an unloaded railway car,operation of the brake valve brings the pressure in brake pipe 18 backup to the pre-brake-application level. The increased pressure in thesupply chamber 78 again creates a force imbalance on diaphragm assembly30 since the pressure in control chamber 80 is now lower than that insupply chamber 78. Check valve 70 is closed and no other fluidcommunication exists at this moment between chambers 78 and 80. Thegreater pressure in supply chamber 78 forces diaphragm assembly 30upward against the yielding resistance of spring 104 and past thegenerally central position illustrated in FIG. 1 where valve set 50 isbrought into contact with valve 52. Valve 52 is thus engaged and pushedupward as is valve stem 48. This upward displacement by diaphragmassembly 30 unseats valve 94, whereby fluid at a greater pressure maypass from supply chamber 78 through bores 92, 90 and 96, and conduit 98into control chamber 80. Consequently, pressure in control chamber 80and brake line 20 rises to effect brake release and to move diaphragmassembly 30 back to a position of equilibrium where valves 52 and 90 areclosed. Thus, it will be seen that chambers 78 and 80 are once againcharged at equal pressures and that brake control apparatus 10 is readyfor the next brake application on an unloaded railway car.

When it is desired to set the brakes on a loaded railway car with brakecontrol apparatus 10 shown in FIG. 1, the fluid pressure in brake pipe18 is reduced in the usual manner (typically a staged reduction) byoperation of the brake valve. The same given pressure drop signal inbrake pipe 18 occurs in conduit 86 and supply chamber 78. This drop inpressure in chamber 78 of control valve 12 changes the force balance ondiaphragm assembly 30, which consequently shifts downward from itsgenerally central position as it seeks to regain a position ofequilibrium. As diaphragm assembly 30 shift downward, it simultaneouslytranslates along the axis of valve stem 48. Valve stem 48 remainsstationary as diaphragm assembly 30 slides downwardly therealong becausevalve 94, which is rigidly attached to valve stem 48, remains firmlyseated in plug member 28. However, the downward shift of diaphragmassembly 30 causes disengagement of valve seat 50 from valve 52. Thus,valve 52 opens in opposition to the biasing force of spring 120, whichnormally urges valve 52 into seating engagement within diaphragmassembly 30.

Since valve 52 is now open, fluid communication exists betweencounterbore 44 and chamber 80 through port 118 of guide 114. Hence, thepressure of control chamber 80, which at this moment is higher than thepressure in supply chamber 78 after a given pressure drop signal, ispresent in counterbore 44, as well as in cross bores 60 and 62, andconduit 74. Fluid at the pressure of control chamber 80 thus enterschambers 124 of limiting valve 14. With the assumption that there are nobreakages or leaks in brake line 20 downstream of control chamber 80,the pressure of chamber 80 acting against the lower face of piston 128in opposition to spring 136 holds valve 130 away from its valve seat ina disengaged position. Passageway 131 being open, fluid flows fromchamber 124 into chamber 126 and through passageway 140 to chamber 148of strut cylinder 16. Since the railway car is loaded, the sprung andunsprung portions of undercarriage 168 shown in FIGS. 3 and 4 haveassumed a closer relative position whereby strut cylinder 16 is broughtinto contact with projecting stop 182. Consequently, valve stem 146occupies a slidable position whereby valve 162 is now unseated.Pressurized fluid may thus flow from chamber 148 through bore 152 intochamber 154 and out port 156 to atmosphere. Therefore, fluid at thepressure of control chamber 80 may effectively vent to atmosphere byflowing from chamber 80 past open valve 52 through counterbore 44, crossbore 60, conduit 74, limiting valve 14, choke 142, passageway 140, andstrut cylinder 16.

As the pressurized fluid in control chamber 80 vents to atmosphere, thepressure in chamber 80 drops rapidly to a level below that of supplychamber 78. It is pointed out that since the pressure of supply chamber78 exceeds that of control chamber 80, pressure of chamber 78 inconjunction with the force of retaining spring 72 holds check valve 68closed against the lower pressure of chamber 80, whereby a pressure dumpthrough cross bore 62, counterbore 44, cross bore 60, and conduit 74 toatmosphere is precluded. Consequently, with a constant pressure existingin supply chamber 78 after the given pressure drop signal in brake pipe18, and with the pressure dropping in control chamber 80, diaphragmassembly 30 seeks a position of equilibrium. Equilibrium is achievedwhen the upward force generated by the pressure of supply chamber 78applied to the lower face of diaphragm assembly 30 balances the downwardsum of the force of spring 104 and the force generated by the pressureof control chamber 80 applied to the upper face of diaphragm assembly30. Since the downward force of spring 104 is constant and the forcegenerated by a pressure is directly proportional to the area over whichthat pressure is applied, a given pressure drop over a larger area mustbe balanced by a greater pressure drop over a smaller area. For example,if the ratio of the areas of diaphragm assembly 30 abutting chambers 80and 78 were 1:2, a pressure drop of two (2) psi in chamber 78 would beequalized by a four (4) psi pressure drop in chamber 80 in conjunctionwith a constant spring force. It will be understood that the end areasof movable diaphragm assembly 30 abutting chambers 78 and 80 may beselectively sized to produce the desired relative pressure drops betweensaid chambers.

Diaphragm assembly 30 thus moves upward toward a generally centralposition to close valve 52, thereby halting the decrease of pressure inchamber 80. Note that the pressure in control chamber 80 is preventedfrom falling below a desired safety level by limiting valve 14 because,the counteracting pressure rendering insufficient opposition, adjustablespring 136 would urge valve 130 to close off communication withatmosphere. Therefore, the pressure drop signal actuating the brakes ofa loaded railway car through brake line 20 is larger than that whichoccurred in brake pipe 18 by the inverse ratio of the areas of diaphragmassembly 30 abutting chambers 80 and 78, respectively.

The brakes on a loaded railway car are released in the same manner asare the brakes of an unloaded railway car. Briefly, operation of aremote brake valve (not shown) brings the pressure in brake pipe 18 upto the pre-brake-application level, which consequent pressure increasein supply chamber 78 forces diaphragm assembly 30 upward against theyielding resistance of spring 104 and the relatively lower pressure ofcontrol chamber 80. The upward displacement of diaphragm assembly 30pulls valve stem 48 upward, unseating valve 94, whereby fluid at greaterpressure may pass from supply chamber 78 through bores 92, 90, and 96and conduit 98 into control chamber 80. Pressure in control chamber 80and brake line 20 thus rises to effect brake release and to causediaphragm assembly 30 to move back to a generally central position ofequilibrium where valves 94 and 52 are closed. Chambers 78 and 80 beingcharged to the same pressure, brake control apparatus 10 is ready forthe next brake application on a laden railway car.

Referring now to FIG. 2, there is shown a modification of a strutcylinder 16 which may be used with loaded, unloaded or partially loadedrailway cars. FIG. 2 shows a strut cylinder 200, which includes a body202 having an upper chamber 204, a central chamber 206 and a lowerchamber 208. A port 210 in the wall of upper chamber 204 unites withconduit 212, which connects to brake line 20 by means of a teeconnection (not shown). Fluid communication is consequently establishedbetween brake line 20 and chamber 204. A port 214 is also provided inthe wall of middle chamber 206. Port 214 connects central chamber 206with passageway 140 leading to second chamber 126 of limiting valve 14.Lower chamber 208 is constantly open to atmosphere via port 215.

Disposed within strut cylinder 200 and extending through chambers 204,206 and 208 is valve stem assembly 216, comprising valve stem 218 andstrut 220. Piston 222, secured to the upper end of valve stem 218, isslidably disposed within chamber 204. Piston 222 includes a peripheralannular groove having disposed therein O-ring 224. O-ring 224 forms asliding seal between piston 222 and the interior surface of chamber 204to confine pressurized fluid beneath the lower face of piston 222.Spring 226 is disposed within the upper portion of chamber 204, betweenthe upper face of the piston 222 and spring follower 228. The springfollower 228 has a depression in its upper surface for receiving andcentering spring adjusting screw 230, which is threadedly mountedsubstantially centrally through the top end of body 202. Thus, by meansof spring adjusting screw 230, the downward biasing force of spring 226against valve stem 218 may be set to a predetermined value and/oradjusted from the outside of strut cylinder 200 without any disassemblythereof.

A jam nut 232 threadedly engages the exterior end of body 202 to coverand protect the protruding end of spring adjusting screw 230. A lockwasher 234 is placed between jam nut 232 and the top end of the body 202to further secure jam nut 232 under conditions of high vibrationtypically encountered during railway operations.

Valve stem 218 extends downwardly from piston 222 through bore 236,chamber 206 and bore 238 into chamber 208. Bores 236 and 238 arecoaxially oriented. O-ring 240, disposed without a peripheral annulargroove in bore 236, forms a sliding seal with valve stem 218 therebypreventing fluid communication between the chambers 204 and 206. Valvebody 242, intermediately mounted on valve stem 218 within centralchamber 206, seats in bore 238 located in the bottom of chamber 206. Theposition of valve 242 functions to open or close fluid communicationbetween chambers 206 and 208 under certain conditions.

The bottom end of valve stem 218 couples to the upper end of strut 220within chamber 208. The connection between valve stem 218 and strut 220is of the lost motion type, such as pin and slot arrangement 244. Springfollower 246 is secured near the upper end of strut 220. Another springfollower 248 is mounted near the lower end of valve stem 218. Placedbetween srping followers 246 and 248, spring 250 surrounds theconnecting ends of valve stem 218 and strut 220. Consequently, valvestem 218 and strut 220 are telescopingly connected with pin and slotarrangement 244 and biased apart by spring 250.

The remaining portion of strut 220 slidably extends through a coaxialbore 252 located in the lower end of body 202. Contact nut 254 engagesthe reduced and threaded end of strut 220. Accordingly, subject to theamount of extension of strut 220, and thus the position of valve 242,passageway 140 may be either open or closed to atmosphere throughchamber 208.

Having reference momentarily to FIGS. 3 and 4 in conjunction with FIG.2, there is shown a typical location for a strut cylinder 181 which maybe similar to strut cylinder 200. Strut cylinder 200 senses thecondition of railway car loading in a manner generally analogous to thatdescribed hereinbefore. Briefly, strut cylinder 181 is mountedsubstantially vertically on truck bolster 170, which is a sprung portionof railway undercarriage 168. Stop 182, secured to truck side frame 172,an unsprung portion of the undercarriage, projects substantiallyhorizontally beneath the strut of strut cylinder 181. Therefore, strutcylinder 181 senses the condition of loading in railway car 166 as afunction of the relative displacement between the sprung and unsprungportions of railway carriage 169.

When mounted on the railway car undercarriage, strut cylinder 200 isadjusted for operation as follows. Depending upon the setting of contactnut 254, the inward translation of strut 220 causes increasedcompression within spring 250 tending to open valve 242. Thecounteracting force of spring 226 is then set by means of adjustingscrew 230 so that valve 242 is closed. Thus the position of valve 242 isa function of the interaction of springs 226 and 250, and the pressurewithin control chamber 80.

The parts of brake control apparatus 10 when strut cylinder 200 ratherthan strut cylinder 16 is employed as cylinder 181 in FIGS. 3 and 4,function as follows. It will be understood that brake control apparatus10 incorporating the first modification shown in FIG. 2 functionsexactly as was previously described both prior to charging and duringcharging of the train brake system for operation. FIG. 1 depicts controlvalve 12 and limiting valve 14 in a charged and ready condition.

The brake set sequence on an unloaded railway car is substantiallyidentical to that which was described above. Briefly, operation of theremote brake valve drops the pressure in brake pipe 18 as well as insupply chamber 78. This drop in pressure in chamber 78 of control valve12 allows diaphragm assembly 30 to shift downward from its generallycentral position along the axis of valve stem 48. The downwarddisplacement of diaphragm assembly 30 unseats valve 52, allowingpressurized fluid at a higher pressure from control chamber 80 to entercounterbore 44, cross bores 60 and 62, and conduit 74. However, sincethe railway car is unloaded, there is no interaction between the end ofstrut 220 and projecting stop 182 shown in FIGS. 3 and 4 which wouldunseat valve 242 in strut cylinder 200. Consequently, no pressurizedfluid flows through conduit 74, limiting valve 14, passageway 140 orstrut cylinder 200 as this pressure discharge route is blocked.

With two unequal pressures acting upon check valve 68, the greaterpressure of control chamber 80 prevails to unseat spherical member 70thereof. Fluid then passes from control chamber 80 through port 118 andpast open valves 52 and 68 and into supply chamber 78. In this manner,the pressure differential, and hence the pressures, in chambers 78 and80 equalize as diaphragm assembly 30 resumes its central position inwhich valves 52 and 68 are closed.

Since conduit 212 connects chamber 204 of strut cylinder 200 with thebrake line 20, chamber 204 experiences a pressure identical to thepressure in chambers 78 and 80 of control valve 12. It will beunderstood that the downward biasing force of spring 226 was preset tohold valve 242 closed against the upward force generated by the pressureof chamber 204 exerted over the bottom face of piston 222. Therefore,the brakes on an unloaded railway car are actuated by the identicalpressure drop signal through brake line 20 as occurred in brake pipe 18.

Setting the brakes on a loaded railway car with a brake controlapparatus 10 incorporating strut cylinder 200 also proceeds as wasdescribed before. Operation of the brake valve causes a given pressuredrop signal in brake pipe 18 as well as supply chamber 78. As aconsequence, diaphragm assembly 30 shifts downward from its generallycentral position seeking to regain a position of equilibrium. Thedownward displacement of diaphragm assembly 30 unseats valve 52, whilevalve 94 remains firmly seated. With valve 52 open, fluid at highpressure from control chamber 80 enters bore 44 and passes throughconduit 74, limiting valve 14, and passageway 140 into central chamber206 of strut cylinder 200.

Since railway car 166 is now loaded, the sprung and unsprung portions ofundercarriage 168 occupy a closer relative position whereby projectingstop 182 has pushed strut 220 into strut cylinder 200 causing increasedcompression within spring 250 tending to push valve stem 218 upward,which in turn compresses spring 226. With valve stem 218 and strut 220thus relatively closer, valve stem assembly 216 occupies a positionwherein valve 242 is unseated. Hence, pressurized fluid may flow throughpassageway 140, past open valve 242 and out port 215 to atmosphere.Therefore, fluid at the pressure of control chamber 80 may effectivelyvent to atmosphere by flowing from control chamber 80, past open valve52 through conduit 74, limiting valve 14, passageway 140 and strutcylinder 200.

It will be understood that chamber 204 of strut cylinder 200 experiencesthe pressure of control chamber 80 through conduit 212 connected tobrake line 20. Hence, the pressure in chamber 204 is decreasing and thusrendering less opposition to spring 226. Consequently, valve 242 staysopen so long as spring 250 together with the pressure in chamber 204overcomes spring 226.

As it vents to atmosphere, the pressure in control chamber 80 dropsrapidly to a level below that of supply chamber 78. Check valve 68remains closed as a consequence. Since the force generated by a givenpressure drop over a larger area neutralizes the force generated by agreater pressure drop over a smaller area, diaphragm assembly 30 thusmoves toward a generally central position to halt the decrease ofpressure in chamber 80 by closing valve 52. Note that the pressure incontrol chamber 80 is prevented from falling below a desired safetylevel by limiting valve 14, as discussed previously. Therefore, thepressure drop signal actuating the brakes of a fully laden railway carthrough brake line 20 is larger than that which occurred in brake pipe18 by the inverse ratio of the areas of diaphragm assembly 30 abuttingchambers 80 and 78, respectively.

The primary advantage in using strut cylinder 200 with brake controlapparatus 10 is realized when applying brakes to a partially loadedrailway car. As usual, operation of the brake valve causes a givenpressure drop signal to occur in brake pipe 18 and supply chamber 78.With less pressure now in supply chamber 78, diaphragm assembly 30shifts downward from its former position of equilibrium, unseating valve52, while valve 94 remains firmly closed. Pressurized fluid at the stillhigher pressure of control chamber 80 is allowed to pass open valve 52into bore 44 and through conduit 74, limiting valve 14 and passageway140, into chamber 206 of strut cylinder 200. Chamber 204 of strutcylinder 200 is constantly open to brake line 20 via conduit 212; thus,both chambers 204 and 206 of strut cylinder 200 are in fluidcommunication with chamber 80 of control valve 12.

Since the railway car is only partially loaded, stop 182 pushes strut220 into body 202 a relatively lesser distance causing increasedcompression of spring 250 tending to push valve stem 218 upward.Consequently, strut 220 and valve stem 218 assume closer relativepositions whereby spring 226 is compressed. The resultant compression ofspring 250 exerts an upward force on valve stem 218 which lifts valve242 from its seat. Accordingly, the pressure in control chamber 80 dropsas it vents to atmosphere through passageway 140, bore 238, chamber 208and port 215 to an initial level corresponding to a loaded railway car.Since chambers 204 and 80 are in fluid communication, pressuresimultaneously decreases in chamber 204 resulting in a correspondinglydecreasing force component in opposition to spring 226. Thus, thedecreased pressure within control chamber 80 eventually renders spring226 effective to move valve 242 toward a closed position, as if therailway car were unloaded. Were the pressure in control chamber 80 todrop to a predetermined safety level, limiting valve 14 would functionas previously described to prevent any further pressure loss. Therefore,the pressure drop signal actuating the brakes of a partially loadedrailway car through brake line 20 is initially the brake signalcorresponding to a loaded car and finally a relatively smaller brakesignal corresponding to an unloaded car. It will be understood that thebrake signal response depends upon the degree of partial railway carloading.

The ability of strut cylinder 200 to tailor the braking signal inrelation to the extent of railway car loading comprises a significantfeature. It is again pointed out that strut cylinder 200 may bescheduled in two ways. First, with spring adjusting screw 230, spring226 may be preset to close valve 242 when the pressure in controlchamber 80 drops to a predetermined level. Second, by means of contactnut 254, the point of engagement with projecting stop 182 may be presetto compensate for the differing empty weights of various type railwaycars.

The release of the brakes on a loaded, unloaded or partially loadedrailway car proceeds exactly as was described above. Briefly, operationof the remote brake valve brings up the pressure in brake pipe 18 andsupply chamber 78, which forces diaphragm assembly 30 upward to unseatvalve 94 while holding valve 52 closed. Fluid is thus allowed to enterchamber 80 through conduit 98 until chambers 78 and 80 equalize andvalves 94 and 52 are closed in anticipation of the next brakeapplication.

Turning now to FIG. 5, there is shown a brake control apparatus 300incorporating a second embodiment of the invention. Brake controlapparatus 300 comprises a control valve 302, a pressure limiting valve304 and a strut cylinder 306. Brake control apparatus 300 is interposedbetween a brake pipe 18 and a brake line 20. Brake pipe 18 runs alongthe entire train length of railway cars and is connected to a remotesource of fluid under pressure (not shown) by means of a brakeapplication valve (not shown). The brake line 20 connects brake controlapparatus 300 with a conventional brake cylinder (not shown).

Control valve 302 is of sectionalized casing construction, consisting ofan upper casing section 308, an intermediate casing section 310 and alower casing section 312. Casing sections 308, 310 and 312 and securedtogether. Plug member 314 is threadedly engaged through the top end ofupper casing section 308.

Disposed within control valve 302 is diaphragm assembly 316. Diaphragmassembly 316 includes a spaced pair of diaphragms 318 and 320. The outerperiphery of first diaphragm 318 is clamped between the lower face ofintermediate casing section 310 and the upper face of lower casingsection 312. Similarly, the outer periphery of second diaphragm 320 isclamped between the lower face of upper casing section 308 and the upperface of intermediate casing section 310.

The inner peripheries of diaphragms 318 and 320 are secured withindiaphragm assembly 316. The inner periphery of first diaphragm 318 isclamped between the lower face of diaphragm follower 322 and the upperface of lower diaphragm nut 324, which threadedly engages a downwardlyprotruding threaded portion of diaphragm follower 322. In a similarmanner, the upper face of diaphragm follower 322 includes an upwardlyprotruding threaded portion threadedly engaged by upper diaphragm nut326 to securely clamp the inner periphery of second diaphragm 320therebetween. Thus, it will be seen that diaphragms 318 and 320 flexiblysuspend diaphragm assembly 316 for limited axial translation within thesloped annular space 325 between diaphragm assembly 316 and intermediatecasing section 310.

Diaphragm follower 322 includes coaxial bore 328. Bore 328 extendsthrough diaphragm follower 322, between the protruding end portionsthereof. The top end of bore 328 unites with counterbore 330 of upperdiaphragm nut 326. Diaphragm nut 326 further includes bore 332positioned intermediate first counterbore 330 and second counterbore334. Consequently, there is a passage through diaphragm assembly 316made up of coaxial bores and counterbores.

By virtue of its placement within control valve 302, diaphragm assembly316 separates the interior volume thereof into two chambers, 336 and338. Pressure supply chamber 336 is defined as that volume between thelower surface of diaphragm assembly 316, and casing section 312. Theeffective area of diaphragm assembly 316 abutting pressure supplychamber 336 is thus the area across the mouth of casing section 312.Coil spring 340 is disposed within chamber 336 intermediate lowerdiaphragm nut 324 and spring follower 342. The spring follower 342 has adepression in its bottom surface for receiving and centering springadjusting screw 344, which is threadedly mounted substantially centrallythrough lower casing section 312. Thus, by means of spring adjustingscrew 344, the upward spring bias against diaphragm assembly 316 may beset to a predetermined value and/or adjusted from the outside of controlvalve 302 without disassembly thereof. A protective jam nut 346threadedly engages the exterior protruding end of spring adjusting screw344 to lock it in any desired position. Gasket 348, placed between jamnut 346 and the exterior of casing section 312, forms a seal to preventpressure leakage from supply chamber 336. Located in the wall of lowercasing section 312, port 350 connects supply chamber 336 with conduit352, leading to brake pipe 18. Consequently, fluid communication existsbetween pressure supply chamber 336 and brake pipe 18.

On the other side of diaphragm assembly 316, control chamber 338 isdefined by the upper surface of diaphragm assembly 316, in conjunctionwith upper casing section 308 and plug member 314. It is pointed outthat the effective area of the upper end of diaphragm assembly 316abutting control chamber 338, due to the enlarged mouth of casingsection 308, exceeds the effective area of the other end of diaphragmassembly 316 which abuts supply chamber 336. Port 354 located in thewall of casing section 308 provides direct fluid communication betweencontrol chamber 338 and a brake cylinder (not shown) by means of brakeline 20.

Plug member 314 includes a bore 356 positioned between and coaxial withcounterbores 358 and 360. Upper counterbore 358 includes a port 362, towhich is connected conduit 364 leading to pressure accumulator 366. Line368, connected between conduit 364 and brake line 20, includes a checkvalve 370, which in its simplest form may consist of a spherical valvemember confined by a transverse pin and a choked passageway in line 368.

Valve assembly 372 is disposed within control chamber 338 between plugmember 314 and upper diaphragm nut 326. Valve assembly 372 includes avalve stem 374. The lower end of valve stem 374 has a rigid valve body376 which seats on bore 332 in diaphragm nut 326. The upper end of valvestem 374 is flexibly coupled to valve body 378 to allow limited axialtranslation therebetween. Valve body 378 is positioned in counterbore358 for seating engagement with one end of bore 356 in plug member 314.Spring 380, which surrounds valve stem 374 between a collar thereon andplug member 314, urges valves 376 and 378 into seated engagement withbores 332 and 356, respectively. In addition, port 382 in the wall ofupper diaphragm nut 326 allows for constant fluid communication betweenthe interior thereof and control chamber 338.

A second check valve 384, which may comprise in its simplest form aspherical valve member positioned between a transverse pin and a chokedpassage, is positioned in line 386. Line 386 is connected between brakeline 20 and conduit 352. By means of conduits 388 and 390, which teeinto line 386 on opposite sides of check valve 384, limiting valve 304and strut cylinder 306 are connected in parallel across check valve 384.

Limiting valve 304 includes a body 392 defining first and secondchambers 394 and 396. First chamber 394 connects to the brake pipe sideof check valve 384, while second chamber 396 connects to the brakecylinder line of check valve 384. Choke 398 functions to restrict therate of fluid flow between chamber 396 and conduit 386.

Piston 400, slidably positioned within first chamber 394, has aperipheral annular groove in which is disposed an O-ring 402. O-ring 402forms a sliding seal between piston 400 and the interior surface of body392 so as to prevent leakage of fluid under pressure between the leftand right portions of first chamber 394. Positioned in the right portionof chamber 394, intermediate the top of piston 400 and spring follower404, is spring 406. Spring 406 is biased to counteract the forcegenerated by the pressure in the left portion of chamber 394 actingagainst the bottom face of piston 400. The force exerted by spring 406may be preset or adjusted by means of spring adjusting screw 408. Springadjusting screw 408 is threadedly mounted between the opposite end ofbody 392 and contacts spring follower 494. Consequently, it will beunderstood that conduit 388 may fluidly communicate with conduit 390through chambers 394 and 396 subject to the action of valve 395.

Strut cylinder 306 includes a body 410 in which is disposed an extendingstrut 412. The body 410 includes a top chamber 414 separated from bottomchamber 416 by bore 418. Conduits 388 and 390 are ported, respectively,to chambers 414 and 416 of strut cylinder 306. Lower bore 420, which iscoaxial with bore 418, slidably engages and guides strut 412 fortranslation. An O-ring 422 is provided within a peripheral annulargroove of bore 420 to form a sliding seal with strut 412 so as toprevent leakage of pressurized fluid from chamber 416. The bottom end ofstrut 412 is reduced and threaded to receive contact nut 424. Valve body426, attached near the top of strut 412, is located in top chamber 414.A spring 428, between the end of chamber 414 and valve body 426, urgesstrut 412 downwardly. Preferably, contact nut 424 should be adjusted sothat valve 426 is open when the car is loaded at between 40% and 60%capacity. Accordingly, subject to the position of strut 412 and thusvalve 426, fluid communication may exist between chambers 414 and 416.

The parts of brake control apparatus 300 illustrated in FIG. 5 and sofar described function as follows. It will be understood that brakecontrol apparatus 300 functions both prior to charging and duringcharging of the train brake system for operation as previously describedwith regard to brake control apparatus 10. FIG. 5 depicts control valve302 and limiting valve 304 in a charged and ready condition.

When it is desired to set the brakes on an unloaded railway car usingbrake control apparatus 300, the pressure in brake pipe 18 is reduced inthe usual manner (typically a staged reduction) by operation of thebrake valve. The same pressure decrease is also experienced in conduits352 and 390, as well as in supply chamber 336 of control valve 302.Since the railway car is unloaded, the sprung and unsprung portions ofundercarriage 168 shown in FIG. 4 do not occupy a closer relativeposition which would cause stop 182 to interact with strut 412 of strutcylinder 306. Strut 412 is thus fully extended closing valve 426 asshown in FIG. 5. Consequently, there is no fluid communication throughstrut cylinder 306. Additionally since during a service brakeapplication, a relatively small pressure drop occurs in the brake pipein comparison to the drop in brake pipe pressure during an emergencybrake application, valve 395 of limiting valve 304 remains closed. Checkvalve 384, under the pressure differential existing between brake line20 and brake pipe 18, is also closed. Consequently, no pressurized fluidflows through check valve 384, limiting valve 304 or strut cylinder 306.

The pressure reduction in supply chamber 336 upsets the force balance ondiaphragm assembly 316, which shifts downward as it seeks to regain aposition of equilibrium. The downward shift of diaphragm assembly 316unseats valve 376, while valve 378 remains closed. Thus, there is directfluid communication between supply chamber 336 through bore 328,counterbore 330, bore 332 and counterbore 334 into control chamber 338.With fluid escaping from chamber 338 to chamber 336, the pressure incontrol chamber 338 drops rapidly toward that of supply chamber 336.Note that valve 378 stays closed biased by spring 380, while thespherical member of check valve 370 is seated due to a pressuredifferential across it. Therefore, the greater pressure stored inaccumulator 366 is disconnected from brake control apparatus 300 at thistime.

As the pressure in control chamber 338 drops, the downward forcegenerated thereby also decreases allowing diaphragm assembly 316 tostart upward. Diaphragm assembly 316 moves upward toward a position ofequilibrium gradually closing valve 376. Equilibrium is achieved whenthe downward force generated by the pressure of control chamber 338,applied to the upper diaphragm assembly 316, balances the upward sum ofthe force of spring 340 and the force generated by the pressure ofsupply chamber 336 applied to the lower face of diaphragm assembly 316.Since the upward force of spring 340 is constant and the force generatedby a pressure is directly proportional to the area over which thatpressure is applied, a given pressure drop over a larger area must bebalanced by a greater pressure drop over a smaller area. For example, ifthe ratio of the areas of diaphragm assembly 316 abutting chambers 336and 338 were 1:2, a pressure drop of four (4) psi in chamber 336 inconjunction with a constant spring force would be equalized by a two (2)psi pressure drop in chamber 338. The end areas of movable diaphragmassembly 316 abutting chambers 336 and 338 may be selectively sized toproportion the relative pressure drops between said chambers as desired.Consequently, diaphragm assembly 316 moves upward, closing valve 376 andhalting the decrease of pressure in control chamber 338. Therefore, thepressure drop signal actuating the brakes of an unloaded railway carthrough brake line 20 is smaller than that which occurred in brake pipe18 by the inverse ratio of the areas of diaphragm assembly 316 abuttingchambers 338 and 336, respectively.

Note that should the given pressure drop signal in brake pipe 18 exceeda predetermined limit, such as during an emergency brake application,spring 406 of limiting valve 304 would be rendered effective to opennormally closed valve 395. Consequently, limiting valve 304 serves as anoptical safety device to bypass control valve 302, applying the brakesof an unloaded railway car with the greater pressure reduction of brakepipe 18 under emergency conditions. Adjustment of spring adjusting screw408 schedules limiting valve 304.

When it is desired to release the brakes of an unloaded railway car,operation of the brake valve brings the pressure in the brake pipe 18up. The increase in the pressure in supply chamber 336 and the force ofspring 340 again creates a force imbalance on diaphragm assembly 316.Diaphragm assembly 316 moves upward against the nominal yieldingresistance of spring 380 to engage and close valve 376. The upwarddisplacement of diaphragm assembly 316 overrides the lost motionconnection between valve 378 and valve stem 374 to open valve 378allowing fluid communication with pressure accumulator 366.Consequently, pressure in control chamber 338 and brake line 20 rises toeffect brake release and to move diaphragm assembly 316 back to aposition of equilibrium where valves 376 and 378 are closed. However,due to the different surface areas of diaphragm assembly 316 abuttingchambers 336 and 338, the rate of pressure rise in brake line 20 is lessthan that in brake pipe 18. For example, if the ratio of the areas ofdiaphragm assembly 316 abutting chambers 336 and 338 were 1:2, thepressure rise in brake line 20 would take place at one-half the rate ofpressure rise in brake pipe 18. It will be understood that the pressurein accumulator 366 never falls below the pressure in brake supply line18, since check valves 370 and 384 would open to allow brake pipe 18 torecharge accumulator 366. Pressure accumulator 366 should be ofsufficiently large volume so that the pressure drain or draw-downexperienced to release the brakes does not exceed some nominal value,two (2) psi for instance, thereby substantially preserving the pressurereservoir therein. Therefore, it will be seen that chambers 336 and 338are once again charged at equal pressures and that brake controlapparatus 300 is ready for the next brake application on an unladenrailway car.

When it is desired to set the brakes on a loaded railway car with brakecontrol apparatus 300, the pressure in brake pipe 18 is reduced in theusual manner (typically a staged reduction) by operation of the brakevalve. The same pressure decrease is also experienced in conduits 352and 390, as well as in supply chamber 336 of control valve 302. However,since the railway car is loaded, the sprung and unsprung portions ofundercarriage 168 shown in FIGS. 3 and 4 occupy a closer relativeposition causing stop 182 to contact strut 412 and thus open valve 426of strut cylinder 306. Consequently, a direct line of communicationexists from conduit 390 through strut cylinder 306 to conduits 388 and386. Therefore, the pressure drop signal actuating the brakes of aloaded railway car through brake line 20 is identical to that whichoccurred in brake pipe 18.

With regard to releasing the brakes on a loaded railway car, there beinga direct open circuit between brake pipe 18 and brake line 20, operationof a remote brake valve (not shown) brings up the pressuresimultaneously in brake pipe 18 and brake line 20. Brake release is thuseffected, and brake control apparatus 300 is ready for the next brakeapplication on a laden railway car.

Referring now to FIG. 6, there is shown a modification of strut cylinder306 which may be used with unloaded, loaded or partially loaded railwaycars. FIG. 6 shows a strut cylinder 450, which includes a body 452having an upper chamber 454, a central chamber 456 and a lower chamber458. A port 460 in the wall of central chamber 456 unites with conduit388, while port 462 in the wall of chamber 458 unites with conduit 390.

Disposed within strut cylinder 450 and extending through chambers 454,456 and 458 is valve stem assembly 464, comprising valve stem 466 andstrut 468. Piston 470, secured to the upper end of valve stem 466, isslidably disposed within chamber 454. Piston 470 includes a peripheralannular groove having disposed therein O-ring 472. O-ring 472 forms asliding seal between piston 470 and the interior surface of chamber 454to confine pressurized fluid beneath the lower face of piston 470.Spring 474 is disposed within the upper portion of chamber 454, betweenthe upper face of the piston 470 and spring follower 476. Springfollower 476 includes a depression in its upper surface for receivingand centering spring adjusting screw 478, which is threadedly mountedsubstantially centrally through the top end of body 452. Thus, by meansof spring adjusting screw 478, the downward biasing force of spring 474against valve stem 466 may be set to a predetermined value and/oradjusted from the outside of strut cylinder 450 without any disassemblythereof. A jam nut 480 threadedly engages the exterior end of body 452to cover and protect in protruding end of spring adjusting screw 478. Alock washer 482 may be placed between jam nut 480 and the top end ofbody 452 to further secure jam nut 480 under conditions of highvibration typically encountered during railway operations.

Valve stem 466 extends downwardly from piston 470 through bore 484,chamber 456 and bore 486 into chamber 458. Opening 488 also connectschambers 454 and 456. Bores 484 and 486 are coaxially oriented. Valvebody 490, intermediately mounted on valve stem 466 within centralchamber 456, seats in bore 486 located in the bottom of chamber 456. Theposition of valve 490 functions to open or close fluid communicationbetween chambers 456 and 458 under certain conditions.

The bottom end of valve stem 456 couples to the upper end of strut 468within chamber 458. The connection between valve stem 466 and strut 468is of the lost motion type, such as pin and slot arrangement 492. Springfollower 494 is secured near the upper end of strut 468. Another springfollower 496 is mounted near the lower end of valve stem 466. Placedbetween spring followers 494 and 496, spring 498 surrounds theconnecting ends of valve stem 466 and strut 468. Consequently, valvestem 466 and strut 468 are telescopingly connected with pin and slotarrangement 492 and biased apart by spring 498.

The remaining portion of strut 468 slidably extends through coaxial bore500 located in the lower end of the body 452. O-ring 502, disposedwithin a peripheral annular groove in bore 500, forms a sliding sealwith strut 468 to prevent pressure leakage from strut cylinder 450.Contact nut 504 engages the reduced and threaded end of strut 468.Accordingly, subject to the amount of extension of strut 468, and thusthe position of valve 490, conduits 388 and 390 may or may not be influid communication.

It will be understood that strut cylinder 450 senses the condition ofrailway car loading in a manner similar to that of strut cylinder 200,which was earlier discussed. When used with strut cylinder 450, brakecontrol apparatus 300 is adjusted for operation as follows. Dependingupon the setting of contact nut 504, the inward translation of strut 468causes increased compression within spring 498, tending to open valve490. The counteracting force of spring 474 is then set by means ofadjusting screw 478 so that valve 490 is closed. Thus, the position ofvalve 490 is a function of the interaction of springs 474 and 498, andthe pressures within control chamber 338 and supply chamber 336. It willbe understood that brake control apparatus 300 incorporating themodification shown in FIG. 6 functions similarly to that previouslydescribed both prior to charging and during charging of the train brakesystem for operation. FIG. 5 depicts control valve 302 and limitingvalve 304 in a charged and ready condition.

The brake set sequence on an unloaded railway car is substantiallysimilar to that which was described above. Briefly, operation of thebrake valve drops the pressure in brake pipe 18, conduits 352 and 390,as well as in supply chamber 336 of control valve 302. Since the railwaycar is unloaded, the sprung and unsprung portions of undercarriage 168do not occupy a closer relative position causing stop 182 to contactstrut 468 of strut cylinder 450. Strut 468 is thus fully extended,closing valve 490 as shown in FIG. 6. Consequently, there is no fluidcommunication through check valve 384, limiting valve 304, nor throughstrut cylinder 450. With a pressure supply chamber 336 now lower thanpressure in control chamber 338, diaphragm assembly 316 shifts downward,opening valve 376. With direct fluid communication between chambers 336and 338, the pressure in control chamber 338 drops rapidly toward thatof supply chamber 336. Since the force generated by a smaller pressuredrop over a larger area neutralizes the force generated by a givenpressure drop over a smaller area, diaphragm assembly 316 thus movesupward to close valve 376, halt the decrease of pressure in chamber 338,and resume a position of equilibrium. Therefore, the pressure dropsignal actuating the brakes of an unloaded railway car through brakeline 20 is smaller that that which occurred in brake pipe 18 by theinverse ratio of the areas of diaphragm assembly 316 abutting chambers338 and 336, respectively.

Setting the brakes on a loaded railway car with strut cylinder 450 inbrake control apparatus 300 also proceeds as was described before.Briefly, operation of the brake valve causes a given pressure reductionin brake pipe 18, conduits 352 and 390, as well as in supply chamber 336of control valve 302. Since the railway car is loaded, the sprung andunsprung portions of undercarriage 168, shown in FIGS. 3 and 4, occupy acloser relative position whereby projecting stop 182 has pushed strut468 into strut cylinder 450, causing increased compression within spring498 tending to push valve stem 466 upward, which in turn compressesspring 474. It will be appreciated that when the railway car is fullyloaded, spring 498 is compressed to an extent sufficient to overcomespring 474 independently of the pressure in chamber 454. Of course, atthis point the pressure in control chamber 338 and thus chamber 454 isdecreasing and rendering less opposition to spring 474. With valve stem466 and strut 468 thus relatively closer, valve stem assembly 464 is sopositioned that valve 490 is unseated. With open fluid communicationbetween conduits 388 and 390, the fluid follows the path of leastresistance so that the pressure drop signal actuating the brakes of afully loaded railway car through brake line 20 is identical to thepressure drop signal in brake pipe 18.

The primary advantage in using strut cylinder 450 with brake controlapparatus 300 is evident when applying brakes to a partially loaded car.As usual, operation of the brake valve causes a given pressure drop tooccur in brake pipe 18, conduits 352 and 390 and supply chamber 336 ofcontrol valve 302. Less pressure now present in supply chamber 336,diaphragm assembly 316 shifts downward from its former position ofequilibrium, unseating valve 376. With direct fluid communicationbetween chambers 336 and 338, the pressure in control chamber 338 beginsdecreasing.

Since the railway car is only partially loaded, stop 182 pushes strut468 into body 452 a relatively lesser distance, causing increasedcompression of spring 498, tending to push valve stem 466 upward.Consequently, strut 468 and valve stem 466 assume closer relativepositions whereby spring 474 is compressed. Note, however, that theresulting compression of spring 498 exerts an upward force on valve stem466 which partially lifts valve 490 from its seat. Accordingly, initialfluid communication exists between conduits 388 and 390 through chambers456 and 458 of strut cylinder 450 as if the railway car were fullyloaded. Since chamber 454 fluidly communicates with control chamber 338via chamber 456, conduits 388 and 386 and brake line 20, pressuresimultaneously decrease in chamber 454. Consequently, the decreasingpressure of control chamber 338 in control valve 302 eventually rendersspring 474 of strut cylinder 450 effective to move valve 490 toward aclosed position, as though the railway car were unloaded. Note that werethe pressure in brake pipe 18 to drop to a predetermined emergencylevel, limiting valve 304 would function as previously described toapply the full brake pipe pressure drop regardless of the degree ofloading in the railway car with strut cylinder 450. Therefore, thepressure drop signal actuating the brakes of a partially laden railwaycar through a brake line 20 in initially the brake signal correspondingto a loaded car and finally a relatively smaller brake signalcorresponding to an unloaded car.

The ability of strut cylinder 450 to tailor the braking signal inrelation to the extent of railway car loading comprises a significantadvantage. It is again pointed out that strut cylinder 450 may bescheduled in two ways. First, with spring adjusting screw 478, spring474 may be preset to close valve 490 when the pressure in controlchamber 338 drops to a predetermined level. Second, by means of contactnut 504, the point of engagement with projecting stop 182 may be presetto compensate for various empty weights of various type railway cars.

The release of the brakes on a loaded, unloaded or partially loadedrailway car proceeds exactly as was described before. Briefly, operationof the brake valve increases the pressure in brake pipe 18, conduit 352and 390, and supply chamber 336. Check valve 384 experiences a pressuredifferential and opens to allow fluid at the higher pressure of supplychamber 336 to enter control chamber 338 by means of lines 386 and 20.Simutaneously, diaphragm assembly 316 moves upward to close valve 376,whereby the pressures in chambers 336 and 338 equalize in anticipationof the next brake application.

If desired, strut cylinder 450 together with check valve 384 can beconnected between brake pipe 18 and brake line 20 without utilizingcontrol valve 302. Preferably, limiting valve 304 is used with checkvalve 384 and strut cylinder 450.

Thus, it is apparent that there has been provided in accordance with theinvention a brake control apparatus for railway cars that fullysatisfies the objects and advantages set forth above. While theinvention has been described in conjunction with specific embodimentsand modifications thereof, it is evident that many other alternatives,modifications and variations will be apparent to those skilled in theart in view of the foregoing description. Accordingly, it is intended toembrace all such alternatives, modifications and variations as fallwithin the spirit and scope of the invention.

What is claimed is:
 1. A method of controlling the pressure droptransmitted from a pressurized train brake pressure supply line with abrake valve therein to a pressurized brake cylinder line of a railwaycar with sprung and unsprung portions, comprising the steps of:(a)connecting a first chamber to the brake pressure supply line; (b)connecting a second chamber to the brake cylinder line; (c) movablyabutting the first and second chambers with diaphragm means havingsurfaces of different areas, with the relatively larger are abutting thesecond chamber; (d) interconnecting the first and second chambers with afirst valve means responsive to the relative positioning of the sprungand unsprung portions of the railway car, which positioning correspondsto the loading condition, to permit fluid flow between the first andsecond chambers when the railway car is loaded so that the brakecylinder line experiences a pressure drop substantially equal to that inthe brake pressure supply line; (e) providing a second valve meansresponsive to predetermined positioning of the diaphragm means to permitfluid flow between the first and second chambers while the first valvemeans is closed and the diaphragm means is unbalanced so that the brakecylinder line on an unloaded railway car experiences a pressure droprelatively smaller than that experienced in the brake pressure supplyline by the inverse ratio of surface areas of the diaphragm meansabutting the second and first chambers, respectively; and (f)interconnecting the first and second chambers with a first check valvemeans responsive to pressure differential for equalization upon apressure rise in the brake pressure supply line so that the railway carbrakes can be released.
 2. The method of claim 1 including the stepof:connecting across the first valve means a normally closed safetyvalve which opens responsive to a predetermined pressure drop in thebrake pressure supply line to permit direct fluid communication betweenthe brake pressure supply and brake cylinder lines.
 3. The method ofclaim 1 including the steps of:applying to the first valve means avariable bias urging said first valve means closed, said variable biascomprising the difference between the pressure in the brake cylinderline and an opposing predetermined bias; and applying to the first valvemeans a bias urging the first valve means open, said opening biascomprising the difference between the pressure in the brake pressuresupply line and a variable bias proportional to the extent of railwaycar loading, so that the brake cylinder line on a partially loadedrailway car initially experiences a pressure drop equal to that for afully loaded railway car, but which finally experiences a pressure dropequal to that for an unloaded railway car.